Processes for the selective oxidation of lower alkanes to oxygenates are known.
Some processes involve the oxidation of alkanes to carboxylic acids. For example, U.S. Pat. No. 4,131,741 describes the production of oxygenated organic compounds such as acetic acid by oxygenating a C3 to C7 saturated aliphatic hydrocarbon in the liquid phase with molecular oxygen in the presence of an inert reaction medium and a cobalt catalyst. The process is designed to minimize the reduction of Co+3 to Co+2. In this process, the butane to oxygen weight ratio is 3.4:1. No promoter is used. The '741 patent contrasts its process with processes using promoters and states that the induction period can be substantially eliminated during batch operation with or without catalyst recycle and continuous operation maintained without the addition or recycle of a promoter when not less than 5% and not more than 90% of the cobalt is in the +3 oxidation state.
U.S. Pat. No. 4,337,356 describes the continuous cobalt catalyzed liquid-phase oxidation of butane to acetic acid. This process used ethanol, methyl ethyl ketone and ethanol, and acetaldehyde as promoters. The water concentration, the iron concentration, and the succinic acid concentration in the catalyst recycle stream are carefully controlled, as is the oxygen concentration in the reactor effluent. The iron concentration is limited to less than 1000 ppm because higher amounts are said to kill the oxidation of butane. The iron comes from corrosion of the stainless steel reaction system.
U.S. Pat. No. 4,859,798 discusses the liquid phase oxidation of alkanes at relatively low temperatures using heteropolyacids or polyoxoanions promoted with azide or certain metals.
EP 0 126 488 describes a process for the liquid phase oxidation of C3 to C13 alkanes using oxygen, a cobalt catalyst, and a catalyst promoter such as acetaldehyde at elevated temperature and pressure. The process can be controlled to make specified products such as carboxylic acids, dialkyl ketones, alkyl esters, and alkanols.
U.S. Pat. No. 7,456,313 involves the liquid phase oxidation of hydrocarbons in the presence of an oxidation catalyst to form an oxidation product. The process is performed in the presence of solvent having a boiling point of at least 25° C. and Hildebrand solubility parameter no greater than 14 MPa1/2. The catalyst is either a solid heterogeneous mixed metal oxide catalyst or a liquid catalyst dissolved in the solvent. The solvent can be a fluorinated organic compound, selected silicones or siloxanes and silicone or siloxane polymers, and hydrophobic ionic liquids.
Other processes for the conversion of alkanes to alcohols and ketones involve the use of solid catalysts. For example, U.S. Pat. No. 7,214,837 teaches a process for the production of a mixture of alcohols and ketones by the liquid phase oxidation of higher alkanes using a catalyst system consisting of transition group metals and a support in the presence of alkyl hydroperoxide.
US 2012/0201743 describes a process for preparing oxygenate products by direct conversion of C1 to C3 alkanes in the gas or liquid phase. The alkanes are contacted with hydrogen peroxide or a hydroperoxy species in the presence of a gold-based heterogeneous catalyst on a metal oxide support in the form of nanotubes, nanofibers, nanowires, or nanorods.
However, solid catalysts are generally less active and less selective, and they may promote the formation of acid-which is not desirable for the production of alcohols or other partially oxidized products.
Current alkane dehydrogenation technology which converts alkanes to alcohols operates at high temperatures and has high capital and operating costs. For example one process utilizes a heterogeneous solid catalyst containing platinum and operates at high temperatures, e.g., above 550° C.
Therefore, there is a need for a process for converting alkanes to alcohols which does not use expensive catalysts and which does not operate at high temperatures.